Place a microphone onto a stand. More often than not, dynamic microphones are used for this purpose because of their ability to withstand high sound pressure levels.
Set the microphone anywhere from right up against the speaker grill to 12 inches away. Experiment with this distance to determine the best position for the microphone you are using.
Position the microphone so that it is pointing toward the center of one of the speakers of the bass amp. This will capture a present and clear sound from the bass amp. However, this can sometimes place too much pressure on the microphone, causing it to distort.
Position the microphone slightly to one side of a speaker in the bass amp. This will capture a slightly more rounded and less present sound. It will also place less pressure on the microphone, preventing the microphone from overloading if the bass amp is turned up very loud.
Position the microphone at a 45-degree angle toward the center of a speaker in the bass amp. This angle will help capture more bass from the amp. This placement will also put less pressure on the microphone, preventing it from overloading if placed in front of a very loud bass amp.